Even git reset --hard might not help. First we
need fetch origin, which is slightly different from
pull, as it will not try to merge. To reset repository to our
remote master we need to reset it hard specifying
reset point to origin/master.

After this operation all uncommited changes will be lost

Reset to origin/master

git fetch origin
git reset --hard origin/master

When in detached head state, also issue commands:

git checkout master
git pull

To bring Your head back to the master. These words
sounds a bit sinisterly.